An inference engine for the semantic web

1
An inference engine for the semantic web

• Naudts Guido
• Student at the Open University
• Netherlands

2
Case study
3
The layers of the semantic web
4
SGML and HTML
SGML and HTML HTML is an application of SGML.
An application is a set of SGML tags and
attribute . The tags are used for the
presentation of the document. Here's a simple
HTML document lthtmlgt ltheadgt
lttitlegt My home page lt/titlegt lt/headgt
ltbodygt lth1gtHello there!lt/h1gt
ltpgt ltfont color"blue"gtWelcome to my
home page!lt/fontgt lt/pgt lt/bodygt
lt/htmlgt
5
XML Properties

• Meta-language
• Subset of SGML
• Definition of tags standardisation?
• Hierarchical
• Namespaces mix of languages!

6
XML Example

• lt?xml version"1.0 ?gt
• lt!DOCTYPE book SYSTEM "http//somesite.org/book.
  dtd"gt
• ltbook id"nielsen01"gt
• lttitlegt
• Designing Web Usability
• lt/titlegt
• ltinfogt
• ltkeygt
• Design
• lt/keygt
• ltkeygt
• Internet
• lt/keygt
• ltisbngt
• 1-56205-810-X
• lt/isbngt 
• lt/infogt
• lt/bookgt

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DTD Example

• lt!DOCTYPE book
• lt!ELEMENT book (title, subtitle?, author,
  info) gt
• lt!ATTLIST book id CDATA REQUIRED gt
• lt!ELEMENT title PCDATA gt
• lt!ELEMENT subtitle PCDATA gt
• lt!ELEMENT author PCDATA gt
• lt!ELEMENT info (key, isbn) gt
• lt!ELEMENT key PCDATA gt
• lt!ELEMENT isbn PCDATA gt
• gt

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XML Schema example
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The layers of the semantic web
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Basics of RDF

• Anything can be a resource.
• Resources have URIs.
• Resources have properties.
• Properties have values and types.
• An RDF document makes statements about resources
  and their properties.

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RDF Properties

• RDF is a language gt
• syntax and semantics
• XML syntax
• Notation 3 syntax

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A Simple Example

• Jan Hanford created the J.S. Bach homepage.
• The J.S. Bach homepage is a resource
• It has a URI (http//www.jsbach.org)
• It has a property
• The property has a type of creator
• The property has a value of Jan Hanford

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RDF Graph
Property Type
Resource
Property Value
has the creator
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Translated to (simplified) RDF
Resource
ltRDFgt ltDescription about"http//www.jsbach.org"gt
ltCreatorgtJan Hanfordlt/Creatorgt lt/Descriptiongt
lt/RDFgt
Property Value
Property Type
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Namespaces added
ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/22-r
df-syntax-ns" xmlnsdc"http//purl.org/DC/"gt lt
rdfDescription about"http//www.jsbach.org/"gt
ltdcCreatorgtJan Hanfordlt/dcCreatorgt lt/rdfDescri
ptiongt lt/rdfRDFgt
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RDF Schema
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RDF Schema example

• lt!-- Id animal.rdf,v 1.2 2001/10/01 001234
  amdus Exp --gt
• lt!-- A simple RDF file for parser testing --gt
• ltrdfRDF
• xmlnsrdfs"http//www.w3.org/2000/01/rdf-schema
  "
• xmlnsrdf"http//www.w3.org/1999/02/22-rdf-synta
  x-ns"
• xmlnsdaml"http//www.daml.org/2001/03/damloil
  "
• xmlns"http//www.daml.org/2000/12/damloil"gt
• ltrdfsClass rdfID"Animal"gt
• ltrdfslabelgtAnimallt/rdfslabelgt
• ltrestrictedBygt
• ltRestrictiongt
• ltonProperty rdfresource"parent"/gt
• ltcardinalitygt2lt/cardinalitygt
• lt/Restrictiongt
• lt/restrictedBygt
• lt/rdfsClassgt
• lt/rdfRDFgt

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The layers of the semantic web
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Ontology

• Terms used to describe an area of knowledge
• Classes, relationships, properties, subclasses
• Definition of semantics
• Avoid tower of Babel

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The layers of the semantic web
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Closed world assumption

• Case study
• Jos is member of W3C.
• All members of W3C are entitled to recieve
  W3C-mail.
• Therefore Jos is entitled to recieve
  W3C-mail.
• We pose the query
• Can Jim recieve mail from the W3C?
• Jim is not in the list ? answer no!!!
  Because of closed world assumption.

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Open world assumption

• Case study
• I have a list of important internet sites
  site A is on my list ? site A is important.
• Site B is not on my list ? site B is not
  important???
• Conclusion Open World is de default
  assumption,
• Closed World must be
  enforced.

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The layers of the semantic web
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Proof

• Proof validation, not generation
• Simple things a ?b, a thus b.
• validation do the URIs exist, are the steps
  followed in the reasoning valid?

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The layers of the semantic web
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Trust

• Build a web of trust
• Truth trust I believe x
• Absolute truth gt a pinguin is a bird
• Contradictions between trusted parties?

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Structure of the project
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Thesis questions 1

• What is the best way for realising an inference
  engine so that the restrictions that are imposed
  by the structure of the World Wide Web on the
  Semantic Web are met ?
• can meta-logical frameworks be used to specify
  the inference engine of the semantic web?

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Thesis questions 2

• what optimisation techniques can be used?
• how can inconsistencies best be avoided?
• which system of logic should be followed on the
  internet?
• what is the interpretation of the logic i.e. what
  are its semantics?

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Metalogical frameworks

• Logic methodology used to represent other
  logics and to reason about their metalogical
  properties

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Optimisation and consistency

• Reorder clauses
• Limit the search space
• Detect inconsistencies i.e. logic contradiction
  might be violation of constraints

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N3 example part 1

• Id authen.axiom.n3,v 1.2 2001/10/01 001234
  amdus Exp
• _at_prefix log lthttp//www.w3.org/2000/10/swap/loggt
  .
• _at_prefix ltauthengt.
• ltmailtojos.deroo.jd_at_belgium.agfa.comgt member
  lthttp//www.agfa.comgt.
• lthttp//www.agfa.comgt w3cmember
  lthttp//www.w3.orggt.
• lthttp//www.agfa.comgt subscribed
  ltmailtow3c-ac-forum_at_w3.org/gt.
• person member institution.
• institution w3cmember lthttp//www.w3.orggt.
• institution subscribed mailinglist
  logimplies
• person authenticated mailinglist a
  logTruth logforAll person, mailinglist,
  institution.

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N3 example part 2

• Id authen.lemma.n3,v 1.3 2001/10/15 224011
  amdus Exp
• _at_prefix log lthttp//www.w3.org/2000/10/swap/loggt
  .
• _at_prefix ltauthengt.
• _who authenticated ltmailtow3c-ac-forum_at_w3.org/gt
  .

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N3 example part 3

• Generated with http//www.agfa.com/w3c/euler/28
  .061 on Sat Dec 01 021927 GMT0100 2001
• for query http//www.agfa.com/w3c/euler/authen.l
  emma.n3
• given http//www.agfa.com/w3c/euler/authen.axio
  m.n3
• _at_prefix log lthttp//www.w3.org/2000/10/swap/loggt
  .
• _at_prefix lthttp//www.agfa.com/w3c/euler/authengt.
  
• ltmailtojos.deroo.jd_at_belgium.agfa.comgt member
  lthttp//www.agfa.comgt.
• lthttp//www.agfa.comgt w3cmember
  lthttp//www.w3.orggt.
• lthttp//www.agfa.comgt subscribed
  ltmailtow3c-ac-forum_at_w3.org/gt logimplies
• ltmailtojos.deroo.jd_at_belgium.agfa.comgt
  authenticated ltmailtow3c-ac-forum_at_w3.org/gt.
• Proof found for http//www.agfa.com/w3c/euler/au
  then.lemma.n3 in 3 steps (232 steps/sec)